One Trip Bottom Hole Assembly and Method for Milling Casing and Directionally Drilling a Lateral Wellbore

ABSTRACT

A bottom hole assembly and method for cutting a window in a cased, oil and gas wellbore and directionally drilling a lateral wellbore through the window without tripping the bottom hole assembly between milling the window and commencing directional drilling of the lateral wellbore.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/972,628 filed Feb. 10, 2021, the entirety of which is incorporated herein by reference for all purposes.

FIELD OF INVENTION

The present invention relates to downhole tools and methods for directional drilling and creating a lateral wellbore.

BACKGROUND OF INVENTION

A typical oil and gas well being drilled today, especially in shale formations, will have multiple lateral sections called “legs” or “sidetracks” that are started by drilling from an existing wellbore. Using a process referred to sometimes as “sidetracking,” a downhole tool called a “whipstock” is lowered into an existing wellbore on the end of a drill string to a depth at which the leg will be started. Typically, this will be at the kick-off point, which is the depth at which the inclination of the path of the wellbore to be drill will begin to go from generally vertical to a generally horizontal orientation. The whipstock is used to deflect the drill string at an angle toward the sidewall of the wellbore.

In its simplest form, the whipstock is comprised of a surface slanted with respect to the axis of the wellbore. A groove or semicircular depression is formed on its surface to support rotation of the drill string. To avoid being pushed down the wellbore as it is deflecting the drill string, the whipstock is anchored. It can be anchored in a number of different ways. For example, if the whipstock is lowered to the bottom of the vertical wellbore, the whipstock may be anchored in place using cement that is pumped into the wellbore to the base of the whipstock and allowed to set. Alternatively, a whipstock may be anchored mechanically using slips or with a tool like a packer. The anchor may be set in placed before the whipstock is lowered. However, it may also be lowered with the whipstock as part of a whipstock assembly.

After the whipstock is oriented in the correct direction, a window is cut in the wellbore's casing using a window milling assembly on the end of a drill string. A casing is usually comprised of a string of pipe joints—lengths of pipe—joined by threaded connections and may be supported by cement that fills the annulus between the exterior wall of the casing and the interior wall of the borehole. Many different types and configurations of mills and other components making up the milling assembly have been used and are possible. The configuration depends on the requirements of the job, such as the size of the window that is needed, which in turn depends on the tools that will need to be passed through it, the build angle of the sidetrack, and other considerations and requirements that may be unique to that well. The whipstock deflects the milling assembly toward the casing as the drill string is rotated. Cutting a window may require multiple trips. However, milling assemblies have been developed to handle cutting the window in one trip of the drill string down the hole.

To further reduce the number of trips, a bottom hole assembly comprising the whipstock assembly, milling assemblies, other tools and instrumentation is lowered to the desired depth, oriented by rotating the drill string, and anchored in the wellbore. The milling assembly is then detached from the whipstock and the milling operation commenced by rotating and lowering the drill string. Several methods of anchoring and detaching the milling system are possible. For example, it is common to connect the whipstock assembly to the milling assembly using, for example, a pin or bolt that can be sheered by pulling up on the drill string after the whipstock is anchored.

Once the window is milled, the milling assembly is raised by tripping out the drill string, and a directional drilling bottom hole assembly is attached and lowered into the wellbore to begin drilling the leg or sidetrack through the formation using directional drilling techniques. There are many different approaches to directional drilling and for steering the direction in which the drill bit is oriented.

One common type of directional drilling tool is a “steerable motor.” The output section of the motor is coupled with a cutting head, such as a drill bit. The axis of around which the output and thus also the cutting head deviates from (meaning it has a non-zero angle with respect to) a reference axis, which would be the axis of rotation of the drill string where it connects to the BHA. A measurement-while-drilling (MWD) system in the BHA informs the driller of the orientation of the “tool face,” meaning the direction in which the face of a cutting head is facing. The cutting face of the cutting head extends in directions generally perpendicular to the axis of rotation of the output section of the motor to which it is attached. The drill string is rotated to point the bit in the direction of the planned wellbore. The motor rotates the drill bit without the drill string rotating the drill bit, resulting in a section of wellbore that curves in a direction in which the drill bit's axis of rotation or the “tool face” (the face of the drill bit, for example) is pointing. Operating the tool in this mode, with the motor turning the drill bit and the drill string not being rotated, is referred to as “sliding.” Continually rotating the drill string—referred to as “drill ahead”—continually rotates the direction of the cutting face being rotated through all possible directions as it is cutting, resulting in a straight bore.

Conventional ways of creating the non-zero angle of the output section of a “steerable motor” include connecting the motor to a drill string through a bent sub or by employing a bent housing below the power section that houses a transmission connecting an end of a rotor in the power section to the output section of the motor and supports bearings for the motor's output section. Both approaches may also be combined in the same BHA. A bent sub results in portion of the BHA below the bent sub—including the motor's power section and output section, and the cutting head connected with the output section—rotating about an axis that deviates from the axis of rotation of the drill string. A bend in the housing of the motor results in the output section of the motor being supported for rotation about an axis that is at an angle to the axis of rotation of the power section of the motor. The motor that is used is typically a so-called “mud motor.” A mud motor is powered by flow of drilling fluid pumped from the surface under high pressure, down through the drill string. The power section of a conventional mud motor typically employs a Moineau progressing-cavity design. The end of its rotor both rotates and revolves in an eccentric fashion about the central axis of the power section. It is connected to the motor's output section using, for example, a universal joint located within a housing section. Bearings are mounted in the housing section so that it rotates about a fixed axis.

SUMMARY

Disclosed below are features and aspects of apparatus and methods for enabling cutting a window in wellbore casing and drilling a lateral wellbore through the window using a steerable bottom hole assembly without requiring the drill string to be removed from the wellbore between cutting the window and directionally drilling the lateral wellbore.

In one, representative embodiment, a bottom hole assembly comprises a downhole motor assembly with an output coupled with a cutting assembly and a whipstock coupled with at least part of the cutting assembly. The motor assembly is adapted for being locked during orientation of the whipstock downhole, so that its output section does not rotate with respect to the drill string. The BHA is configured to change downhole the angle of the axis of rotation of the motor's output section relative to the axis of rotation of the drill string. During cutting of the window, the angle of rotation of the motor's output section is at a first angle. It can then be changed to a second angle that is not zero and is greater than the first angle for directional drilling of the lateral wellbore.

In a representative example of the method, a bottom hole assembly capable of cutting a window in a wellbore's casing and directionally drilling a lateral wellbore through the window is lowered into the wellbore on a drill string until it reaches a planned kick-off point. The bottom hole assembly comprises a motor, a cutting assembly, and a whipstock. The output of the motor is locked at the surface or downhole to enable orienting the whipstock toward the planned window by rotating the drill string. After the whipstock is anchored, the BHA is separated from the whipstock. A window in the casing and a rat hole are formed by rotating the cutting assembly by rotating the drill string, or by unlocking and operating the motor, or both. The BHA is configured so that the angle of rotation of an output section of the motor is set to a first angle relative to axis of rotation of the drill string where it connects to the BHA, the first angle being suitable for forming the window and the rat hole. After cutting of the window and forming a rat hole, the BHA is reconfigured downhole, without “tripping” the drill string to remove the BHA from the wellbore, to change angle of the axis of rotation of the output section to a second angle that is greater than the first angle and not zero degrees to make the BHA steerable for directionally drilling the lateral wellbore.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation of a simplified, bottom hole assembly.

FIG. 2A is schematic representation of the bottom hole assembly of FIG. 1 in a cased wellbore before it is anchored.

FIG. 2B is schematic representation of the bottom hole assembly of FIG. 2A after a whipstock is separated from the bottom hole assembly.

FIG. 2C is schematic representation of the bottom hole assembly of FIG. 2A during cutting of a window in the casing of the wellbore.

FIG. 2D is schematic representation of the bottom hole assembly of FIG. 2A after enlargement of the window's opening and during formation of a rat hole.

DETAILED DESCRIPTION

In the following description of representative embodiments and examples of the claimed subject matter, like numbers refer to like parts.

The following description discloses representative, non-limiting embodiments of a downhole tool capable of operating in a milling mode to cut a window in wellbore casing and then changing to a directional drilling mode in which the face of the tool rotates off-axis to allow the tool to be steered.

The tool is configured so that, in the milling mode, it is capable of, orienting and setting a whipstock, cutting a window in the wellbore's casing, and creating a rat hole, after which it can be changed to a directional drilling mode by adjusting the tool from having no bend to having a bend that changes the orientation of the tool face from zero degrees, which is oriented along the axis of the drill string, to a non-zero degree angle without having to remove the BHA from the wellbore.

In the simplified, representative embodiment schematically illustrated by FIG. 1 and the slightly more detailed drawing of this representative embodiment illustrated in FIGS. 2A-2D, a bottom hole assembly 100 comprises a motor 102, such as a mud motor, with a power section 103 and rotational output section 104, to which is connected at least a portion of a cutting assembly 106. Sub 105 couples directly or indirectly the motor 102 to a drill string 107 or, alternatively, to another tool or assembly which is connected to the drill string. A whipstock assembly 108 connects to a lower end of the cutting assembly at a releasable connection point 110. The whipstock assembly comprise a whipstock 112 and anchor 114. The BHA 100 may further comprise other types tools, such as a measurement-while-drilling (MWD) system, stabilizers, drill collars, and other components that are not shown or indicated. These additional tools and components may be placed between one or more of the tools and other components shown in the illustration or elsewhere in the BHA. Please note that the drawings are not to scale.

The cutting assembly 106 is configured to cut an opening and mill edges of the opening to enlarge it into a window in a wellbore's casing large enough to accommodate a drilling of a lateral wellbore through the adjacent rock formation. As mentioned above, the assembly may take many different configurations; the illustrated configuration is merely representative. The configuration of the cutting assembly is determined, in part, by the size of the window that needs to be cut, the type and size of casing, and other requirements. The cutting assembly 106 is further configured to allow it to be used for directional drilling a wellbore through the formation.

The representative example of the cutting assembly 106 that is illustrated comprises a cutting head 116 or drill located at the lower end of the assembly. It has shape and arrangement of cutting elements on its cutting face and sides capable of milling the casing to cut an initial opening in the casing and drilling a bore hole through the surrounding rock formation. To enlarge the initial opening formed by the cutting head 116, the cutting assembly 106 also comprises one or more string or “watermelon” mills 118 a, 118 b. The mills grind material from edges around the initial opening in the casing using a side-cutting action to enlarge the window. The cutting assembly 106 includes, optionally, one or more “flexible” or “bendable” pipe joints 120 between cutting head 116 and one of the watermelon mills 118 a, 118 b, between the two watermelon mills 118 a, 118 b, and/or between a watermelon mill 118 a, 118 b and, for example, an output section 104 of the motor. A “flexible” or “bendable” pipe joint 120 accommodates a greater amount of bending or flexing than a typical drill pipe without being damaged. As an alternative to an assembly formed by a cutting head separated from a mill using a pipe joint, the cutting head or drill and one or more side-cutting mills could be formed using a single, unitary body, meaning a body that does not have a pipe joint between the cutting head and at least one of them mills. Alternatively, the motor 102 could be located between the cutting head 116 and lower watermelon mill 118 a, or between watermelon mills 118 a and 118 b. In the last example, the cutting assembly 106 would thus be, in effect, split. In alternative embodiments of the assembly, it's components are not contiguous and may be separated by other components of the BHA. Furthermore, the one or more mills comprising the cutting assembly may include one or more mills incorporated with the motor 102, such as by attaching cutting elements or structures to an outer diameter of the housing or integrating cutting structures of a mill into the housing of the power section 103, the output section 104, or both. For example, an alternative embodiment of the cutting assembly may have two or more mills with a side cutting action, one between the cutting head and the motor and another on the motor, or one on the motor and the other above connected into the BHA above the motor.

The motor 102 is any type of motor capable of turning at least the cutting head 116, if not the entire cutting assembly 106, to at least cut an opening in the casing and, if also driving the mills, mill the casing, as well as subsequently to drill through a rock formation. One example is a mud motor. The power section 103 is connected to the output section 104 though a transmission within housing section 124. Bearings mounted in the housing section 124 support the output section 104 so that it rotates about a fixed axis.

As described below, to switch from a window cutting/milling mode to a directional drilling mode, the BHA 100 is adjustable downhole so that an angle of an axis of rotation 126 of the output section 104 of the motor 102 relative to a reference axis can be changed. The reference axis is aligned or coincides with the central axis of the drill string. Generally, the axis of rotation of the output section does not deviate from the central axis of the drill string during orientation of the whipstock and milling. This means that the axis of rotation of the output section 104 is (when the drill string and other flexible portions of the BHA are straight) generally aligned with the central axis of the drill string and forms a zero-degree angle with respect to the reference axis. Although normally set at zero, this angle could be set to a non-zero angle (such as at the surface or downhole) during cutting and/or milling the opening for the window. This angle will be less than one degree in most applications.

To convert to directional drilling setting or mode, the angle of the BHA is changed to a second angle different from the first angle that is non-zero with respect to the central axis of the drill string. The second angle is greater than the first angle and is suitable for directionally drilling a lateral wellbore for oil and gas production. The second angle is, in one embodiment, over one degree, depending on the planned trajectory of the lateral wellbore. The adjustment of the BHA to switch from the first angle to the second angle can be introduced or made above, below, or both above and below the power section 103. For example, either or both the sub 107 and the housing 124 can be configured to allow for introduction of a bend downhole. In one embodiment, the deviation angle of the BHA is set, at the surface, to zero degrees or another angle suitable for cutting and/or milling the window before it is run into the wellbore.

The BHA comprises means capable of changing downhole the deviation angle of a cutting head with respect to a drill string from a first angle suitable for the cutting and/or milling of the window to a second, non-zero angle for directional drilling. The means may, optionally, allow for more than two angles or for a range of angles. The means may, optionally, also be capable of changing the deviation angle from a non-zero angle to a zero-degree angle downhole. Examples of such means include rotatable sections of the BHA that introduce and, optionally, remove a bend in the BHA, such as in a section or sub above the motor or a housing section below the power section of the motor. To activate the means to change the deviation in the BHA downhole, the drill string can be pulled, pushed, and/or rotated, or a hydraulic or electric setting tool is actuated.

The motor 102 is, in at least one embodiment, lockable, meaning that its output section 104 can be locked at least at the surface (or, optionally, downhole) and unlocked remotely when it is downhole. While locked, the output section 104 is prevented from rotating relative to the drill string, preventing rotation of the components of bottom hole assembly 100 that are connected to and below the output section 104. After it is unlocked, output section 104 and all components connected below it may rotate with respect to the drill string from the surface. For example, the motor 102 could be locked by a bolt or pin that is sheered by rotation of the rotor (caused by pumping fluid through the motor 102), actuating a hydraulic or electric setting tool, or pulling, pushing and/or rotating the drill string. It may also be locked using, for example, a sleeve that is shifted or rotated to unlock the rotor using such methods. However, no specific means for locking and unlocking is required, except one capable of being selectively unlocked downhole for operation of the motor following orientation of the whipstock, as described below.

Turning now to FIGS. 2A-2D, the figures illustrate the BHA 100 at different stages of cutting a window in casing of a wellbore before the BHA is converted downhole to a directional drilling mode. Though the method is shown and described with reference to the BHA 100, the method described below can be practiced with a different BHA that is specially configured or adapted to perform, or otherwise capable of performing, the steps of the method.

FIG. 2A illustrates BHA 100 is lowered on an end of a drill string (not shown) into an existing wellbore that has been cased with steel casing 200. The casing may have also been cemented into placed. The side wall of the wellbore and any cement in the annulus between the outer diameter of the casing 200 and the side wall of the wellbore is not indicated. In this example, a plug 202 has been set within the wellbore. The whipstock anchor 114 will be connected to the plug 202 to anchor the whipstock 112. However, the method is not limited to a specific way of anchoring whipstock.

Once the whipstock 112 is lowered to the kick-off point for the planned lateral, it is rotated in the direction of the planned lateral by rotating the drill string and anchoring it. The motor 102 is locked during orientation of the whipstock 112 to allow the drill string to be rotated from the surface to orient the whipstock 112. The motor 102 is locked at the surface, before it is lowered into the wellbore, or it is locked downhole. In this example, attaching the anchor 114 to the plug 202 anchors the whipstock 112 in a manner that prevents its movement downwardly and rotationally. If the whipstock 112 is to be separated from the cutting assembly by pulling on the drill string, the anchoring also prevents upward movement of the whipstock 112.

While the whipstock 112 is being oriented, the BHA is set so that the axis of rotation 126 of the output section 104 of the motor 102 does not deviate from the central axis of the drill string. It is preferred, though not required, that the BHA is set at zero degrees at the surface.

At some point after the whipstock anchor 114 is anchored in place, whipstock 112 is separated from the BHA, as shown in FIG. 2B. The way the whipstock is separated depends on how the whipstock 112 is joined by connection 110 to the cutting assembly 106, examples of which are described above.

Turning to FIG. 2C, the step of cutting a window in casing 200 then commences by rotating the cutting assembly 106 and lowering the drill string to cause the whipstock 112 to deflect the cutting assembly toward the inner wall of casing 200 to cut a hole 204 in the casing with cutting head 116.

The opening is then enlarged to form a window, as indicated by FIG. 2D, by watermelon mills 118 a and 118 b or other means for milling away the casing around opening 204 created by cutting head 116. While the opening 204 is being enlarged, the cutting head 116 begins to form a rat hole 206. In the illustrated example, there is a lower watermelon mill 118 a connected to an upper watermelon mill 118 b by a length of flexible pipe 120 a. However, the method is not limited to this example; other arrangements of cutting bits and mills are possible.

During cutting and milling of the window, the axis of rotation 126 of the output section 104 is, preferably, set at zero degrees. To rotate the cutting assembly 106 (indicated in FIG. 1), the drill string is rotated from the surface by, for example, a top drive, though other means to rotate the drill string can be used. The motor 102 remains locked to permit the drill string to rotate the cutting assembly. Alternatively, the cutting assembly is rotated by running the motor 102 after the motor is unlocked.

After the opening 204 is milled to form the window and the rat hole 206 is finished, the deviation angle of the BHA is changed to a non-zero angle suitable for steering the face of the cutting head 116 along a planned trajectory for the wellbore. When changing the angle the cutting assembly may be pulled back into the wellbore or it may be changed in the rate hole. 

What is claimed is:
 1. A method of drilling a lateral wellbore by sidetracking from an existing, cased wellbore, comprising the steps of: connecting a bottom hole assembly (BHA) to a drill string, the bottom hole assembly comprising: a motor coupled with the drill string, the motor comprising a power section and output section, wherein the motor is adapted to allow locking of the motor to prevent rotation of the output section relative to the motor and unlocking the motor to allow for rotation; a cutting head coupled with the output section of the motor; one or more mills for enlarging an opening formed by the cutting head; and a whipstock assembly releasably connected to the cutting head; wherein the BHA is adapted for remotely changing while downhole a deviation of an axis of rotation of the output section of the motor with respect to a central axis of the drill string from a first angle for cutting and milling a window in a casing string to a second, non-zero-degree angle for directional drilling; lowering the BHA on the drill string into a previously cased wellbore; once the BHA is at a depth for a planned window in a casing string in the wellbore, rotating the drill string with the motor locked, while the deviation of the axis of rotation of the output section is set at zero degrees, to orient the whipstock; anchoring the whipstock in the wellbore; releasing the whipstock from the BHA; lowering the BHA toward the whipstock to cause the cutting head to deflect toward the casing string; rotating the cutting head to cut an opening in the casing string and to form a rat hole; rotating the at least one mill to enlarge the opening; without raising the BHA to the surface, changing the deviation of the axis of rotation of the output section of the motor to the second, non-zero-degree angle for directional drilling; and directionally drilling the wellbore with the motor unlocked and the axis of rotation of the output section of the motor in the second, non-zero-degree angle.
 2. The method of claim 1, further comprising: orienting a cutting face of the cutting head along a planned trajectory by rotating the drill string from the surface; and powering the motor with the motor unlocked to rotate the cutting assembly.
 3. The method of claim 1 wherein the deviation of the axis of rotation of the output section of the motor is set to the first angle prior to lowering the BHA into the wellbore.
 4. The method of claim 1 wherein the motor is locked prior to lowering the BHA into the wellbore.
 5. The method of claim 4 wherein the motor is unlocked to begin direction drilling of the wellbore.
 6. The method of claim 1 wherein during at least a portion of a period in which the cutting head is cutting the opening or the at least one mill is enlarging the opening the motor is locked, and the cutting head is rotated by rotating the drill string from the surface.
 7. The method of claim 1, wherein the motor is unlocked and powered to rotate the cutting head to cut the opening.
 8. The method of claim 1, wherein the motor is locked against rotation during milling and the cutting head is rotated by rotating the drill string.
 9. The method of claim 1, wherein the BHA comprises a means for changing the deviation of the axis of rotation of the output section of the motor to the second, non-zero angle for directional drilling.
 10. The method of claim 1 wherein the BHA comprises at least one of an adjustable sub coupling the motor to the drill string and a motor with an adjustable lower housing, the adjustable sub being configured to change downhole the deviation of the output section of the motor from the first angle to the second, non-zero-degree angle, and the adjustable lower housing being configured to change downhole the deviation of the output section of the motor from the first angle to the second, non-zero-degree angle.
 11. The method of claim 9, wherein changing the deviation of the axis of rotation of the output section of the motor to the second, non-zero-degree angle for directional drilling comprises pulling, pushing or rotating the drill string from the surface.
 12. The method of claim 9, wherein changing the deviation of the axis of rotation of the output section of the motor to the second, non-zero-degree angle for directional drilling comprises pumping drilling fluid down the drill string.
 13. The method of claim 9, wherein changing the deviation of the axis of rotation of the output section of the motor to the second, non-zero-degree angle for directional drilling comprises actuating a setting tool in the BHA.
 14. The method of claim 1 wherein at least one of the one or more mills is coupled with the output section of the motor.
 15. The method of claim 1 wherein at least one of the one or more mills is coupled with the power section of the motor to rotate with the power section of the motor.
 16. A bottom hole assembly (BHA) for sidetracking from an existing wellbore, the bottom hole assembly comprising: a motor coupled with a drill string, the motor comprising a power section and a lockable output section adapted for unlocking downhole; a cutting head coupled with the output section of the motor; one or more mills for enlarging an opening formed by the cutting head; and a whipstock assembly releasably coupled to the cutting head; wherein the BHA is adapted for selectively changing while downhole a deviation of an axis of rotation of the output section of the motor with respect to a central axis of the drill string from a first angle for cutting an opening for a window to a second, non-zero-degree angle for directional drilling; the BHA further comprising at least one of an adjustable sub coupling the motor to the drill string and a motor with an adjustable lower housing, the adjustable sub being configured to change downhole the deviation of the output section of the motor from the first angle to the second, non-zero degree angle, and the adjustable lower housing being configured to change downhole the deviation of the output section of the motor from zero degrees to a non-zero-degree angle.
 17. The bottom hole assembly of claim 16 wherein the BHA changes the deviation of the axis of rotation of the output section of the motor to the second, non-zero-degree angle for directional drilling in response to movement of the drill string to which it is attached, the movement comprising one or more of pulling, pushing or rotating the drill string.
 18. The bottom hole assembly of claim 16 wherein the BHA changes the deviation of the axis of rotation of the output section of the motor to the second, non-zero-degree angle for directional drilling in response to drilling fluid being pumped through the BHA.
 19. The bottom hole assembly of claim 16 wherein the BHA changes the deviation of the axis of rotation of the output section of the motor to the second, non-zero-degree angle for directional drilling in response to actuation of a setting tool in the BHA. 